1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for performing coating processing of a resist solution or developing processing, for example, for a substrate such as a semiconductor wafer, a glass substrate for a liquid crystal display, or the like.
2. Description of the Related Art
In a photolithography process in the process of fabricating a semiconductor device, for example, resist coating processing of forming a resist film on the surface of a wafer, exposure processing of exposing the wafer by irradiating a pattern on the wafer, developing processing of developing the exposed wafer, heating processing and cooling processing before the coating processing, before and after the exposure processing, and after the developing processing, and the like are performed. Such processing is performed in processing units provided individually, and these processing units are unified to compose a coating and developing processing system so as to continuously perform such successive processing.
Generally, the coating and developing processing system is composed of a loader/unloader section for carrying a wafer into/out of the coating and developing processing system, a processing section having a coating processing unit, a developing processing unit, a thermal processing unit, and the like and performing the majority of the aforesaid wafer processing, an aligner outside the system for subjecting the wafer to exposure processing, and an interface section, provided adjacent to the processing section and the aligner, for delivering the wafer between the processing section and the aligner.
When the wafer is processed in this coating and developing processing system, in order to prevent impurities such as fine particles from adhering to the wafer, air cleaned by an air purifier or the like is supplied as down-flowing air into the coating and developing processing system, while an atmosphere inside the coating and developing system is exhausted, whereby the wafer can be processed in a clean condition.
Moreover, to realize sensitive exposure, a chemically amplified resist is used. The chemically amplified resist has a basic polymer insoluble in an alkaline developing solution, for example, and an acid generator, and obtains high resolution by causing polarity changes in an exposed portion and an unexposed portion by the use of a catalytic reaction of an acid. In the aligner, a circuit pattern is exposed in a resist film by using a mask, and an elimination reaction is caused to a protective group which protects a hydroxyl group of the basic polymer by the acid produced at this time. Thereafter, the wafer is transferred to the thermal processing unit, where the catalytic reaction of the acid is accelerated to quicken the elimination reaction by PEB (post-exposure baking) which is heating after exposure, and thereby the exposed portion, for example, is made soluble in the alkaline developing solution. The wafer is then transferred to the developing processing unit and the portion which is made soluble is removed by the developing solution, whereby a precise circuit patter is obtained.
In recent years, however, exposure technology in which a beam with a shorter wavelength is used is being developed to form a finer and more precise circuit pattern, and when the beam with the shorter wavelength is used, it is confirmed that impurities at molecular level such as oxygen, basic substances, ozone, and vapor which have been insignificant so far exert a bad influence on the formation of the precise circuit pattern. Specially when the impurities adhere to the wafer on the occasion of exposure, an appropriate pattern is not exposed, and thus a drop in yield can not be avoided.
Accordingly, it is necessary for the impurities not to adhere to the wafer under processing, but the use of clean air as before is inappropriate because the air itself contains impurities such as oxygen.
An acid produced at the time of exposure has high reactivity, and hence shows a neutralization reaction with basic substances in air during the transfer of the wafer. In this case, the acid is deactivated, which causes a change in the formation of a slightly soluble surface layer and the line width of the circuit pattern. The elimination reaction of a protective group depends on the temperature, and some kind of chemically amplified resist causes the elimination reaction of the productive base by a catalytic reaction of the acid, for example, even in the state of an ordinary temperature. Therefore, there is the possibility that the elimination reaction progresses during transfer before PEB, which causes pattern deformation, the deterioration of reproducibility, and the like.
Even in such pattern deformation as can be conventionally ignored, there is still room for improvement in these days when a more precise circuit pattern is demanded, but such clean air and system configuration as before can not meet the demand.
Moreover, the wafer comes and goes between the processing section and the exposure processing section via the interface section. There is the possibility that the neutralization reaction of the acid or the elimination reaction of the productive base occur after exposure as described above, while the acid is not produced before exposure, and consequently the conditions of an atmosphere inside the interface section demanded before and after exposure are different. Thus, the formation of the optimum atmosphere for the condition of the wafer after exposure in the interface section is demanded.